1. Field of the Invention
The present invention relates to a rotation synchronous control system for use in controlling magnetic disk drives for the purpose of magnetic disk drives for the purpose of, for example, operating the spindle motors of a plurality of magnetic disk drives, which are called a array drive, synchronously in rotation with each other.
A recent tendency for demanding, in a computer system, a transfer of large amount of data at high speed, and therefore, storage drives such as magnetic disk drives also require a transfer of large of amount of data of high speed which communicate data with a host computer.
2. Description of the Related Art
In general, in a single unit of a magnetic disk drive, a data transfer speed is limited by a rotation speed of a motor which rotates a magnetic disk as a record medium. Accordingly, if it is intended to attain a high speed operation by increasing a data transfer speed, it is necessary to perform a read/write operation by driving a plurality of disk drives, called a disk array drive, simultaneously and in parallel. At this time, according to a command from a host computer, the spindle motors of the magnetic disk drives are synchronously rotated in parallel, so that it becomes possible to perform a parallel transfer of data.
The present invention refers to a strategy for realizing high speed data transfer by accurately executing a rotation synchronous function, which is called spindle sync, in such array drive, etc.
FIG. 1 is a block diagram of a prior-art array disk system. In FIG. 1, the reference numeral 1 denotes a controller (host unit), 2 a magnetic disk drive, 3 a spindle sync/reference signal source (oscillator), 4 a sync control, 5 a rotation device, 6 an interface control, 7 a rotation reference position detection control, 8 a receiver (RV), and 9 through 11 connectors (CN).
One of the systems in which a plurality of magnetic disk units is operated synchronously in rotation with each other is already known as a "disk array drive". In this disk array drive, a plurality of magnetic disks are connected to a controller so that they are operated in parallel, data is transferred between them, simultaneously thereby attaining a high speed data transfer.
Also in the disk array drive, a spindle sync (rotation synchronous control) function is provided for the plurality of magnetic disk drives to maintain the spindle sync between the rotation of the devices so that the magnetic disk drives operate as if they were a single unit.
The disk array drive is configured as shown in FIG. 1, for example. As shown in FIG. 1, a plurality of magnetic disk drives 2 are connected to the controller 1 and a spindle sync/reference signal source (oscillator) 3 is connected to each of the magnetic disk drives 2. FIG. 1 shows two magnetic disk drives as indicated with "Unit A" and "Unit B", respectively, but more than two disk drives may be connected to the controller 1 in practice.
Each of the magnetic disk drives 2 is provided with a sync control 4, rotation device 5, interface control 6, rotation reference position detection control 7, and receiver (RV) 8. Each magnetic disk drive 2 is connected to the controller 1 by connecting an interface cable (I/F CABLE) 13 between the connector 9 of each magnetic disk drive 2 and the connector (not shown) of the controller 1.
Also each magnetic disk drive 2 and the spindle sync/reference signal source 3 are connected to each other by connecting a sync signal cable 14 to the connector 10 of each magnetic disk drive 2 and connector 11 of the spindle sync/reference signal source 3. Thus, each magnetic disk drive 2 can be supplied with a spindle sync/reference signal (it will be referred to as "sync signal" hereafter and will be illustrated as "SYNC" in FIG. 1, etc.) from the spindle sync/reference signal source 3.
The rotation device 5 includes a magnetic disk, a spindle motor for driving the rotation of the magnetic disk, etc. and has a magnetic head 12 provided near the rotation device 12. The rotation reference position detection control 7 is provided to detect a rotation reference position signal from the rotation device 5. For instance, it generates a reference signal (e.g., index signal (INDEX)) based on a rotation position (HEAD POSITION) signal read through the magnetic head 12.
The sync control 4 receives a control signal (SC) from the interface control 6, a reference signal (INDEX) from the rotation reference position detection control 7, and a sync signal (SYN) from the spindle sync/reference signal source 3. The sync control 4 controls the rotation device 5 and causes the spindle motor of the rotation device to rotate synchronously with the sync signal.
During operation of the disk array drive thus arranged, the spindle motor of the rotation device 5 is subject to spindle sync control based on the instruction from the controller 1. In this case, the spindle sync/reference signal source 3 supplies a sync signal to each of the magnetic disk drives 2.
In each magnetic disk drive 2, the receiver 8 receives the sync signal through the connector 10 and then supplies it to the sync control 4 which in turn controls the spindle motor of the rotation device 5 such that the spindle motor rotates synchronously with the sync signal.
Thus the rotation devices 5 of the plurality of magnetic disk drives 2 can be rotated synchronously with the sync signal.
As described above, when rotation synchronous control is executed for a plurality of disk drives such as a disk array drive. As shown in the prior art, the sync signal which is defined as a reference signal has to be generated by an external oscillator supplied to each of the disk drives.
The aforementioned prior art array disk system has the following disadvantages:
(1) To perform a spindle sync between the plurality of magnetic disk drives, each of the magnetic disk units is connected by a cable with the sync signal source (spindle sync/reference signal source). Thus, each of the magnetic disk units are provided with a connector.
However, the above-mentioned cables and connectors are apt to incur a fault such as broken conductor, poor connection, etc. If such a fault occurs, the spindle sync between the magnetic disk drives will be lost and the drives will not function properly.
(2) A cable and connectors are used to transmit the reference signal to the magnetic disk drive signal. Recently, however, many of the magnetic disk drives are designed compact and it is difficult to provide the units with such connecting means.
Also if a broken conductor is found in the cable or the connector is found to have a poor connector, it is extremely difficult to locate such a fault. The magnetic disk must be shut down until the fault is located.
(3) If an additional magnetic disk is connected to the aforementioned disk array drive, an additional cable must be connected between the added drive and the sync signal source.
In such a case, the disk array drive must be shut down with the power supply turned off once. Therefore, the disk array drive cannot be used. Also a very long time (for example, more than 10 sec) is required until all of the drives attain a spindle sync again.